QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Seetharam, B. Articles by Li, N. Search for Related Content PubMed PubMed Citation Articles by Seetharam, B. Articles by Li, N.

---

Article

Cellular Import of Cobalamin (Vitamin B-12)^{1 ,2}

Bellur Seetharam^*,3, Santanu Bose^* and Ning Li^*

^* Division of Gastroenterology and Hepatology, Department of Medicine and Biochemistry, Medical College of Wisconsin and Veterans Administration Medical Center, Milwaukee, WI 53226

³To whom correspondence and reprint requests should be addressed.

Recent studies have isolated and characterized human gastric intrinsic factor (IF) and transcobalamin II (TC II) genes, whose products mediate the import of cobalamin (Cbl; Vitamin B-12) across cellular plasma membranes. Analyses of cDNA and genomic clones of IF and TC II have provided some important insights into their sites of expression, structure and function. IF and TC II genes contain the same number, size and position of exons, and four of their eight intron-exon boundaries are identical. In addition, they share high homology in certain regions that are localized to different exons, indicating that IF and TC II may have evolved from a common ancestral gene. Both IF and TC II mediate transmembrane transport of Cbl via their respective receptors that function as oligomers in the plasma membrane. IF-mediated import of Cbl is limited to the apical membranes of epithelial cells; it occurs via a multipurpose receptor recently termed "cubilin," and the imported Cbl is usually exported out of these cells bound to endogenous TC II. On the other hand, TC II-mediated Cbl import occurs in all cells, including epithelial cells via a specific receptor, and the Cbl imported is usually retained, converted to its coenzyme forms, methyl-Cbl and 5'-deoxyadenosyl-Cbl, and utilized.

KEY WORDS: • cobalamin • import • intrinsic factor • transcobalamin II • receptor • epithelial cell

This article has been cited by other articles:

				R. Waibel, H. Treichler, N. G. Schaefer, D. R. van Staveren, S. Mundwiler, S. Kunze, M. Kuenzi, R. Alberto, J. Nuesch, A. Knuth, et al. New Derivatives of Vitamin B12 Show Preferential Targeting of Tumors Cancer Res., April 15, 2008; 68(8): 2904 - 2911. [Abstract] [Full Text] [PDF]

				F. S. Mathews, M. M. Gordon, Z. Chen, K. R. Rajashankar, S. E. Ealick, D. H. Alpers, and N. Sukumar Crystal structure of human intrinsic factor: Cobalamin complex at 2.6-A resolution PNAS, October 30, 2007; 104(44): 17311 - 17316. [Abstract] [Full Text] [PDF]

				J. Wuerges, G. Garau, S. Geremia, S. N. Fedosov, T. E. Petersen, and L. Randaccio Structural basis for mammalian vitamin B12 transport by transcobalamin PNAS, March 21, 2006; 103(12): 4386 - 4391. [Abstract] [Full Text] [PDF]

				J. A. Bauer, B. H. Morrison, R. W. Grane, B. S. Jacobs, S. Dabney, A. M. Gamero, K. A. Carnevale, D. J. Smith, J. Drazba, B. Seetharam, et al. Effects of Interferon {beta} on Transcobalamin II-Receptor Expression and Antitumor Activity of Nitrosylcobalamin J Natl Cancer Inst, July 3, 2002; 94(13): 1010 - 1019. [Abstract] [Full Text] [PDF]